Metallic coating alloy



Patented Oct. 17, (1944 METALLIC COATING AL'LoY Arthur J. Manger, Gary,Ind., and Alfred H. Ward, Brentwood, Pa., assignors to Carnegie-Illinois Steel'Corporation, a corporation of New Jersey No Drawing.Application May 1, 1942,

Serial No. 441,358-

iclaims. (Cl. 75 -178) In accordance with the present invention, thereare provided certain improvements in metal coating compositions of. thekind that are of suitable additional agents to galvanizing bathswhich-will perform the functions of tin at least employed for producingthe so-called galvanized coatings on a ferrous metal base.

It ishighly desirable. in galvanizing operations to produce a'coa-tingwhich is characterized by the appearance of spangles. Also, it isdesirable to employ in the coating compositions elements {which increasethe fluidity of the galvanizing bath.

hot dip zinc coating processes, such as those commonly-referred to asgalvanizing? to use additions of metallic tin to the molten coating bathto improve, the fluidity, and to provide asuitable'set of conditions forproducing a .dis-

tinctive spangled finish. The benefits derived from such additions oftin to the coating baths have been described as being dueto a beneficiating influence of the tin on the surface tension properties duringsolidification of the coating, or to a prolongation of the freezingperiod caused by the presence of a tin-zinc eutectic. The characteristicfinish resulting from the practice embodies a relatively. smooth finishwith an even distribution of the coating on the surfaces of the coatedarticle. Without the addition of tin, the zinc coating tends to formunevenly from place to place on the" object and individual units ofcrystallization in the solidifiedcoating are separated by a network ofdepressed boundary lines Heretofore it'has been the general practice inhave-established that the depth of these depresas satisfactorily as doestin itself.

In the investigations leading up to the present invention, it has beendetermined that metallic lead, which is present as a constituentimpurity in the grade of zinc (known in the trade as Prime WesternSpelter) used in galvanizing operations, is responsible for thedepressed boundaries described -above herein. Also, the

investigations leading to the present invention sions isroughlyproportional to the lead content of the coating. But, since leadimparts a certain degree of fluidity to the bath and also promotes theformation of spangles in the coating, the presence of lead in the bath,instead of being regardedas detrimental in view of the foregoing,

is in fact highly desirable.

The investigations leading to the present invention show further thatthe minimum amount of lead above which attractive spangles can beproduced is about 0.20%. Spangles increase in size roughly proportionalto the lead content until the amount of lead reaches about 1.00%. Atthis percentage the depressions around the spangles are pronounced.

Additionally, the investigationsleading to the present inventionestablish that metallic cadmium' when present in the spelter bath inamounts greater than 0.05% tends to promote the formation of frostyspangles and to miniwhere the coating is relatively thin. In these thinareas, the protection afiorded by the coating is less than that in themajor portion of th surface where the coating is heavier. The additionof tin, in amounts of from substantially 0.25% to 1.00% or even inlarger quantities,

causes the elimination of these depressed boundaries.

The multitudinous applications. of galvanized products are toowell-known to require comment; and it is obvious immediately that thedesirability of obtaining a satisfactory protective coating is of highimportance. However, because of the immediate scarcity of tin, and itshigh strategic value, the use of tin in galvanizing baths has'becomeprohibitive.

Consequently, it is of high importance to find I substitutes for tin inthis particular application,

T which substitutes will not-be prohibitive either from the standpointof economics or from the standpoint of strategic availability.

'Consequently, the present invention is" predicated upon investigationsleading to the finding mize objectionable depressions at the spangleboundaries. This tendency is found to increase with the cadmium contentof the bath up to about 1.00%. The finish produced with cadmium alone,however, is notas attractive or uniform as that of tin-bearing baths.

The investigations leading to the present invention further establishthat antimonyinamounts greater than 0.05% promotes the formation of'thedecorative-spangles even in the absence 'of other alloying constituents.However, unless other additions arepresent, the crystalline growthduring solification is such as to'result in extremely rough surfaceswith portions of the spangles drawn up .above other portions.

In accordance with the present invention,

therefore, it is found thatwith additions of the alloying metals, lead,cadmium and antimony, to

. the galvanizing bath, there may be utilized all the desirablefunctions of each metal, and there is obtained a galvanizing bath with'a fluidity equal to or better than that produced by the addition oftin. Furthermore, in accordance with the present invention, it has beenfound that the disadvantageous eflects oi the individual metals arematerially modified satisfactorily so that there are produced from theimproved bath, coatings which are of equal uniformity and appearanceproduced by the addition of tin, and the coating composition is usablein any standard coating equipment without changing any of theestablished practices'oi cleaning, pickling, or fluxing in any way. -Thedesirable results of the present invention are obtained without the useof tin, and the composition of the bath is such that strategic scarcityof metals employed is obviated.

In practicing the present invention, to commercial Prime Western" zinccontaining substantially 0.70% of lead and up to 0.20% cadmium, there isadded suflicient high purity zinc of electrolytic or equivalent grade toreduce the lead content of the bath to the desired range or 0.25% to1.00%. To this bath then is added sufllcient cadmium metal to obtain acadmium content of g from 0.2% to 1.0 As an alternative to suchprocedure there may be utilized the first drawn condensate from zincretorts which may contain a low lead content of about 0.30% to 0.50%,and a high cadmium content of about 0.25% to 0.35%.

This grade of material may or may not contain 2. A tin-free bath for hotdip galvanizing, having properties of fluidity when molten and alsohaving coating properties at-least comparable to correspondingproperties of a zinc-tin galvanizing bath containing at least 0.25% tin,the said tin-free bath being consisting of principally zinc togetherwith small but efiective amounts of lead, cadmium and antimony.

3. A tin-free bath for hot dip galvanizing, having properties offluidity when molten and also having coating properties at leastcomparable to corresponding properties of a zinc-tin galvanizing bathcontaining at least 0.25% tin, the tin- Iree bath being consisting ofzinc, together with small but efiective amounts of lead, cadmium, andantimony, wherein the lead predominates over the cadmium and antimony.

4. A tin-free bath for hot dip galvanizing, having properties offluidity when molten and also having coating properties at leastcomparable to corresponding properties of a zinc-tin galvanizing bathcontaining at least 0.25% tin, the tinfree bath being consisting of zinctogether with small but efiective amounts of lead, cadmium and antimony,and wherein the lead is present in from approximately 0.5% toapproximately 1% lead, the lead predominating over the cadmium andantimony.

5. A tin-free bath for hot dip galvanizing, having properties offluidity when molten and also having coating properties at leastcomparable to corresponding properties of a zinc-tin galvanizing bathcontaining at least 0.25%tin, the tinfree bath being consisting of zinctogether with small but effective amounts of lead, cadmium, andantimony, wherein the lead does not exceed approximately 1% andpredominates over the cadmium and antimony, there being less antimonythan cadmium.

ARTHUR J. MAUGER. ALFRED H. WARD.

